(1) Field of the Invention
The present invention relates to a method of fabricating a metal electrode of a semiconductor device.
(2) Description of the Prior Art
In line with the increase of the concentration of the density of a semiconductor device, the semiconductor device has become miniaturized and lightened. However, in a semiconductor device, the speed of vertical reduction is lower than the speed of horizontal reduction, and step coverage between each layer forming a semiconductor device is a critical factor regarding efficiency and reliability of a semiconductor device.
Especially, in the case of a thin film transistor used in a flat display device, a method of preventing a metal electrode on a glass substrate from forming differential step has been studied.
In general, a metal process is a latter one among the processes of fabricating a semiconductor device, and when it comes to a thin film transistor of reverse staggered type, a metal process is an initial one for forming a gate electrode on an insulating substrate.
According to a detailed embodiment of the prior art shown in FIGS. 1A or 1B, a metal layer made of chromium Cr and the like is formed on a glass substrate by carrying out a sputtering or chemical vapor deposition (hereinafter CVD), and a desired pattern is then formed by wet etching such that a gate electrode 2 is formed. Subsequently, as a gate insulating layer 3, e.g., a nitride silicon layer is formed by CVD. The above described conventional processes have problems that step coverage of serially deposited layers deteriorates due to the differential step and a satisfactory element cannot be obtained.
Where an insulating layer 4 is formed by partial anodic oxidation of the gate electrode and in forming an insulating layer 4, as shown in FIG. 2B, if another film is deposited thereon by CVD, step coverage would deteriorate, which results in problems of deteriorating reliability and efficiency. The above problems are considered serious in thin film transistors and must be solved.